Turns out, that rtl/amd64/rtlmem.S doesn't currently compile fine with
ML64, and it wasn't included for compilation anyways in the original RTL.
So, just remove it from there as well.
... as it should have always been done (and must be done for NTDLL
and NTOS kernel as well). This allows using the RTL with the correct
definitions and the reduced functionality available at boot-time.
+ Make the RTL main header compatible.
In addition, this will permit re-using existing code that already
uses the RTL (mostly string conversions).
See commits 427c90af3 (r36761) and b46e8cc18 (r36980) for some
background.